1. Field of the Invention
The present invention relates to a thin metallic layer type magnetic recording medium suitable for high density magnetic recording and an apparatus for preparing the same.
2. Description of the Prior Art
Recently, high density magnetic recording technology has been remarkably developed by improvements of a recording and reproducing system, a running system, a magnetic head and a magnetic recording medium in a magnetic recording apparatus. In these developments, the requirement of high density magnetic recording for the magnetic recording medium has been attained by an increase of a coercive force and an increase of a residual magnetic flux density for reducing a thickness of the medium. It has been difficult to increase the residual magnetic flux density over 3,000-4,000 gauss in a conventional magnetic recording medium prepared by coating a mixture of a magnetic powder and a binder. The magnetic recording density could not be further increased. Recently, thin metallic layer type magnetic recording media which do not contain an organic binder have been developed. The thin metallic layer type magnetic recording media have been prepared by forming a thin metallic layer on a substrate by forming metallic particles made of a metal or alloy of iron group element or an alloy thereof with an element other than iron group elements by a vacuum evaporation, sputtering, ion-plating, ion beam evaporation or electrochemical method and depositing the metallic particles on a non-magnetic substrate.
Among these methods, the vacuum evaporation method has been especially developed as the technology for preparing uniform, long magnetic recording media in an industrial scale.
The following methods have been proposed to increase a coercive force and to improve a squareness in the vacuum evaporation method.
(a) a tilt deposition;
(b) a deposition in a magnetic field;
(c) a control by a selection of a material for a base; and
(d) a crystalline growth by a heat treatment.
Among these methods, the most effective practical method is the tilt deposition process disclosed in Japanese Examined Patent Publication No. 19389/1966. In this process, as shown in FIG. 1, a thin metallic layer is formed by a tilt deposition of a metallic particles (1 ) at a tilt angle .theta. to the normal line (3) of a surface of a substrate (2). In this process, if multi-layers are formed at a constant tilt angle .theta., the metallic particles in the multi-layers have orientation in one direction to extend an apparent length so as to improve shape anisotropy whereby a coercive force is increased. However, in order to give the multi-layer structure of the thin metallic layer, the vacuum evaporation must be repeated depending upon number of the layers. Thus, it causes disadvantages of inferior productivity and higher production cost. In order to overcome the disadvantages, the number of the thin metallic layers must be reduced. Thus, the magnetic characteristics and the electro-magnetic conversion characteristics are inferior.